Characterization of canine coagulation factor VII and its complex formation with tissue factor: canine–human cross‐species compatibility

Summary. Background: Canine models have been good predictors of efficacy of hemophilia treatments, including recombinant human coagulation factor (F)VIIa (hFVIIa). However, canine FVIIa and tissue factor (TF) have remained incompletely characterized. Objective: To explore canine–human cross‐species FVIIa–TF compatibility in order to strengthen the predictive value of canine models in research on FVIIa and TF. Methods: Canine FVIIa (cFVIIa) and canine TF_(1–217) cTF_(1–217)] were produced by recombinant techniques, and canine–human cross‐species FVIIa–TF interactions were characterized in vitro. Results: Recombinant cFVIIa and soluble cTF_(1–217) were produced and purified to homogeneity. hFVIIa and cFVIIa bound with comparably high affinities to cTF_(1–217) (K_D = 6.0 ± 0.7 nm and K_D = 6.0 ± 0.3 nm , respectively) and to cell surface‐expressed cTF (K_D = 8.4 ± 0.4 nm and K_D = 7.2 ± 1.2 nm , for ¹²⁵I‐labeled hFVIIa and cFVII, respectively). In contrast, cFVIIa bound to human TF (hTF) with decreased affinity, both in solution and on cell surfaces. The decreased binding resulted in reduced activity of cFVIIa in functional assays with hTF_(1–209). In direct comparison, cFVIIa was more active than hFVIIa, both in the absence and the presence of cognate TF. Conclusion: The present finding that hFVIIa binds to cTF essentially as it does to hTF substantiates the hypothesis that human FVIIa–TF biology can be reliably recapitulated in canine models on administration of hFVIIa to dogs.